Selection of candidate amphibian dermal exposure models for regulatory use

Dermal exposure is a potentially significant but understudied route for pesticide uptake in terrestrial amphibians. Beyond providing protection and minimizing desiccation, the skin of amphibians has unique characteristics for gas and water exchange that make amphibians more susceptible to chemical exposure than other vertebrates. Until recently, evaluation of terrestrial pesticide risk in both amphibians and reptiles was not explicitly considered for ecological risk assessment and was often accounted for by using birds and/or mammals as a proxy. To address the lack of a consensus terrestrial amphibian dermal exposure approach, we collated a database with published measured pesticide tissue concentrations associated with known pesticide application rates. The data set includes tissue concentrations for 11 amphibian species and 12 different pesticides. We then constructed a set of amphibian exposure models, including EFSA and USEPA models for the regulatory assessment of pesticides, parameterized these candidate models and compared their performance. We present the results of the model selection exercise for estimating pesticide exposure in terrestrial amphibians. When evaluating performance, we considered two types of objective functions, binomial classification and distance approaches, to account for differing goals of maximizing protection and statistical accuracy. The classification approach characterizes false negative model predictions as the proportion of under-predicted exposures. The distance approach uses information criteria to statistically find the best approximating model. We present the technical implementation, how to resolve discrepancies between the proposed EFSA and USEPA models, and adaption of the exposure model for differing goals of regulatory screening and population modeling application.